Abstract: A comparative study on the effect of two bisbenzylisoquinolines, tetrandrine (TTD) and berbamine (BBM), and verapamil (VRP) on reversing multidrug resistance was reported. TTD, BBM and VRP showed significant activity in reversing adriamycin (ADR) and vincristine (VCR) resistance in acquired resistant MCF-7/Adr and KBv₂₀₀ cell lines, and the effect was shown to be dose dependent.TTD, at the concentration of 10 μmol·L^-1, completely reversed ADR resistance in MCF-7/adr cells. TTD, BBM and VRP increased intracellular ADR accumulation in MCF-7/Adr cells. There is minor difference in structure between TTD and BBM. TTD showed greater activity than VRP in reversing MDR, while BBM showed similar activity to that of VRP. TTD also showed significant activity in vivo in reversing ADR resistance in MDR MCF-7/Adr solid tumor in nude mice.